1. Field of the Invention
The present invention provides an apparatus and a method for controlling the speed of rotation of a shaft. More particularly, the invention uses an alternator to control the speed of rotation of a shaft driven by an air motor.
2. Description of the Prior Art
U.S. Pat. No. 3,241,948, entitled "Aluminus Metal Particles", the contents of which are herein incorporated by reference, describes an apparatus for forming aluminum particles from molten aluminum. The apparatus has a particle forming unit that includes a centrifugal casting pot mounted on a vertical shaft. The shaft is driven through a pulley and a belt by a motor. In a commercial embodiment, the motor was connected directly to the shaft. An electric motor was used to provide power because it was believed critical to maintain tight tolerance on the speed of rotation of the casting pot.
A problem was encountered with the previously known apparatus when there was a power failure. The rotation of the pot would stop and the molten metal would drip from the pot onto the motor and burn it out. This problem was solved by replacing the electric motor with an air motor. This solution, however, created another problem in that it was not possible to maintain control of the speed of rotation of the pot within desired limits when an air motor was used in place of the electric motor.
Systems are known for maintaining the speed of a driven shaft constant through use of a control which senses the difference between the actual speed of the shaft and a desired value. Such difference is used to generate an error signal that is used to adjust the mechanism driving the shaft so as to obtain the desired output speed. None of these systems, however, uses an alternator to control the speed of rotation of an air driven shaft.
U.S. Pat. No. 3,572,959, entitled "Coupling Controller", and U.S. Pat. No. 4,404,942, entitled "Method of Controlling the Rotational Speed of a Rotary Shaft", are representative of patents describing such systems.